1. Field of the Invention
The present invention relates to a method and an apparatus for optimizing print head speed in an ink jet printer. More particularly, the present invention is directed at the algorithm used to optimize print head speed in a thermal ink jet printer.
2. Description of the Related Art
Today, greater demands are being placed on personal computing systems, be they PC or Macintosh or Unix based. With these increased demands come greater expectations of printers used as a part of the computing systems. Many prior printers do not possess optimized throughput or perform at optimal speeds. This is especially true of thermal ink jet (xe2x80x9cTIJxe2x80x9d) printers. They produce quality results at a price well below that of most laser printers. Thermal ink jet printers even print in color, thus providing a very versatile machine for home and office use. Nevertheless, such printers are not operating at a power level that optimizes throughput.
The present invention overcomes certain deficiencies known in the prior art. For example, commonly-owned U.S. Pat. No. 5,349,905, the contents of which are incorporated herein by reference, discloses a method and apparatus for controlling the power requirements of a printer. This is done by controlling the speed of the sheet transport system in accordance with the image density (xe2x80x9cIDxe2x80x9d) of the image being produced. That is, an image having a high density will print slower than one having a low density. A controller controls the speed of a drive motor driving the transport assembly in accordance with the image density. However, this and other prior systems do not take into account that power consumption cycles of two or more modules of the printer may be out of phase with one another.
Commonly-owned U.S. Pat. No. 5,714,990 also deals with controlling the speed of an ink jet head in a thermal ink jet printer according to image density. A required print time for each swath of printed matter placed on a printed sheet is calculated based on image density. A maximum frequency for the firing of the ink jets is determined based on image density information. Like U.S. Pat. No. 5,349,905, the system of the ""990 patent does not provide controls for altering the behavior when two or more modules simultaneously demand power from sources that are out of phase with each other. Instead, the system of the ""990 patent controls printhead speed on the basis of image density only.
One difficulty of many prior systems is that they only take into consideration the power needs of the print head while ignoring the power needs of the dryer, which generally operates out of phase with the print head. Thus, prior systems are not concerned with the true ideal speed at which a sheet should be fed through a printer. Rather, they provide suboptimum speeds and in turn provide less than ideal productivity.
An important aspect of the present invention overcomes the problems associated with the prior art by providing an algorithm that takes into consideration the possibility that two or more printer modules operate out of phase with each other to determine an optimum speed for feeding a print substrate through a printer. The algorithm dynamically computes an image output terminal""s (IOT""s) real time maximum processing speed, which is constrained by specified available power that satisfies the power needs of the two modules whose power needs correlate with the print density (image area coverage (xe2x80x9cACxe2x80x9d)) and are deterministically out of phase with each other. In calculating the processing speed, the algorithm automatically optimizes the printer""s throughput, while keeping the power within a specified allotment. The algorithm may be applied to a thermal ink jet (xe2x80x9cTIJxe2x80x9d) printer, where a print head module lays ink on a substrate pursuant to the specified area coverage, after which a dryer, e.g. a microwave dryer, dries the liquid portion of the ink on the substrate. Since the maximum power available to both modules is restricted, the process speed reduces as the area coverage increases and vice versa. However, due to a deterministic phase lag in the power requirements, the instantaneous tolerable peak module speeds may differ. Therefore, for optimum throughput, the maximum tolerable peak speeds must be dynamically computed in real time and the IOT is to be operated at the lower of the two speeds.
The optimum speed is achieved by a method including, for example, the steps of calculating a TIJ printer""s maximum speed on a real time basis to optimize the throughput of the TIJ printer so as to maintain the printer""s power consumption within a specified power allotment. An apparatus according to the present invention includes a print head module that lays the ink on a substrate, e.g., a piece of paper, as per the specified area coverage. The substrate is moved towards a microwave (xe2x80x9cxcexcwavexe2x80x9d) dryer, i.e., the dryer module, that dries the liquid portion of the ink on the substrate. Both the print head module and the dryer module consume large amounts of power. Since the maximum power available is limited, the process speed is reduced as the area coverage increases due to the large heating requirements and the large number of drops to be laid. On the other hand, the process speed is increased as the area coverage decreases due to the lower heating requirements and a lower number of drops to be laid.
Owing to the sequential nature of the print and dryer modules, the power requirements of the two modules will be out of phase and, as a result, their instantaneous peak speeds may differ. The optimum process speed is the lower of the two, and the algorithm according to the present invention determines this. Calculation of the speed of the substrate through the dryer module and the printer module is performed using internal control electronics, such as a microprocessor, Random Access Memory (RAM), and/or Read Only Memory (ROM).